Patent Application
20240114613
The disclosure relates generally to ion implantation apparatus and more particularly to high energy beamline ion implanters.
Ion implantation is a process of introducing dopants or impurities into a substrate via bombardment. Ion implantation systems may comprise an ion source and a series of beam-line components. The ion source may comprise a chamber where ions are generated. The ion source may also comprise a power source and an extraction electrode assembly disposed near the chamber. The beam-line components, may include, for example, a mass analyzer, a first acceleration or deceleration stage, a collimator, and a second acceleration or deceleration stage. Much like a series of optical lenses for manipulating a light beam, the beam-line components can filter, focus, and manipulate ions or ion beam having particular species, shape, energy, and/or other qualities. The ion beam passes through the beam-line components and may be directed toward a substrate mounted on a platen or clamp.
Implantation apparatus capable of generating ion energies of approximately 1 MeV or greater are often referred to as high energy ion implanters, or high energy ion implantation systems. One type of high energy ion implanter is termed linear accelerator, or LINAC, where a series of electrodes arranged as tubes conduct and accelerate the ion beam to increasingly higher energy along the succession of tubes, where the electrodes receive a powered voltage signal. Known LINACs are driven by an RF voltage of frequency in the MHz-GHz range.
One issue for operation of RF LINAC ion implanters is that during acceleration of an ion beam, which ion beam is partitioned into ion bunches along a direction of propagation (Z-direction), a natural tendency of an ion bunch is to spread out both transversely (in X-direction and Y-direction) as well as longitudinally (in Z-direction, or equivalently, in time). Known methods for focusing ions are generally complex and may require unduly lengthy acceleration stages to focus the accelerating ion bunches.
In some approaches, transverse focusing of ions may be performed adding DC quadrupoles. These DC quadrupoles may be added at various stages along a LINAC, which stages include drift tube electrodes that are used to accelerate the ion bunches. Such DC quadrupoles may be fabricated as electrostatic or magnetic components that apply a DC quadrupole field to a passing ion beam. The addition of these DC quadrupoles to a LINAC inevitably add cost, size and complexity to the beamline and the associated control systems.
With respect to these and other considerations the present disclosure is provided.
In one embodiment an apparatus is provided. The apparatus may include a drift tube assembly that includes a plurality of drift tubes to conduct an ion beam along a beam propagation direction. The plurality of drift tubes may define a multi-gap configuration corresponding to a plurality of acceleration gaps. The plurality of drift tubes may further define a plurality of RF quadrupoles, respectively, wherein the plurality of RF quadrupoles are arranged to defocus the ion beam along a first direction at the plurality of acceleration gaps, respectively, the first direction extending perpendicularly to the beam propagation direction.
In another embodiment, a linear accelerator may include a buncher to receive a continuous ion beam and output a bunched ion beam; and a plurality of acceleration stages, to accelerate and focus the bunched ion beam. The plurality of acceleration stages may include a first acceleration stage, having a first drift tube assembly that forms a multi-gap configuration corresponding to a plurality of acceleration gaps. The first drift tube assembly may further define a first plurality of RF quadrupoles formed at the plurality of acceleration gaps, respectively. As such, the first plurality of RF quadrupoles may be arranged to defocus the bunched ion beam along a first direction at the plurality of acceleration gaps, respectively, the first direction extending perpendicularly to a beam propagation direction. The plurality of acceleration stages may further include a second acceleration stage, having a second drift tube assembly that forms the multi-gap configuration, where the second drift tube assembly further defines a second plurality of RF quadrupoles formed at the plurality of acceleration gaps, respectively. As such, the second plurality of quadrupoles may be arranged to focus the ion beam at a given gap of the plurality of acceleration gaps along the first direction.
In another embodiment, an ion implanter may include an ion source, to generate a continuous ion beam, and a linear accelerator, comprising a buncher and a plurality of acceleration stages arranged to receive the continuous ion beam and generate a bunched ion beam. The plurality of acceleration stages may include a first acceleration stage, having a first drift tube assembly that forms a multi-gap configuration corresponding to a first plurality of acceleration gaps. The first drift tube assembly may further define a first plurality of RF quadrupoles formed at the plurality of first acceleration gaps, respectively. As such, the first plurality of quadrupoles may be arranged to defocus the ion beam at a given gap of the first plurality of acceleration gaps along a first direction, extending perpendicular to the beam propagation direction. The plurality of acceleration stages may also include a second acceleration stage, having a second drift tube assembly that forms the multi-gap configuration corresponding to a second plurality of acceleration gaps. The second drift tube assembly may further define a plurality of RF quadrupoles formed at the second plurality of acceleration gaps, respectively. As such, the second plurality of RF quadrupoles may be arranged to focus the bunched ion beam at a given gap of the second plurality of acceleration gaps along the first direction.
The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the disclosure. The drawings are intended to depict exemplary embodiments of the disclosure, and therefore are not be considered as limiting in scope. In the drawings, like numbering represents like elements.
An apparatus, system and method in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, where embodiments of the system and method are shown. The system and method may be embodied in many different forms and are not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so this disclosure will be thorough and complete, and will fully convey the scope of the system and method to those skilled in the art.
Terms such as “top,” “bottom,” “upper,” “lower,” “vertical,” “horizontal,” “lateral,” and “longitudinal” may be used herein to describe the relative placement and orientation of these components and their constituent parts, with respect to the geometry and orientation of a component of a semiconductor manufacturing device as appearing in the figures. The terminology may include the words specifically mentioned, derivatives thereof, and words of similar import.
As used herein, an element or operation recited in the singular and proceeded with the word “a” or “an” are understood as potentially including plural elements or operations as well. Furthermore, references to “one embodiment” of the present disclosure are not intended to be interpreted as precluding the existence of additional embodiments also incorporating the recited features.
Provided herein are approaches for improved high energy ion implantation systems and components, based upon a beamline architecture, and in particular, ion implanters based upon linear accelerators. For brevity, an ion implantation system may also be referred to herein as an “ion implanter.” Various embodiments entail novel approaches that provide the capability of improved control of an ion beam during acceleration through the acceleration stages of a linear accelerator, and in particular, improved ion beam focusing.
The apparatus 100 is formed of a plurality of drift tubes (collectively deemed a drift tube assembly), including a first grounded drift tube 102, a second grounded drift tube 108, a first powered drift tube 104, disposed downstream of the first grounded drift tube 102, and a second powered drift tube 106, disposed downstream of the first powered drift tube 104. It may be understood that the drift tube assembly formed by the apparatus 100 is coupled to a resonator (not separately shown), where the resonator is arranged to output an RF signal. In the configuration of
Note that the apparatus 100 is may be arranged to accept the ion beam 130 as a bunched ion beam, where upstream to the apparatus 100 the ion beam 130 may be a continuous ion beam, and may be bunched by a buncher (not shown), arranged according to known LINACs. As such, by properly arranging the timing of the arrival of a bunch of ions of the ion beam 130 at the gap G1A, gap G1B, gap G1C, the ion beam 130 may be accelerated by electric fields that are created when the generated RF voltage on the powered electrodes reach an optimum value and has the right polarity. In this manner, a given bunch may be accelerated generally along the Z-axis of the Cartesian coordinate system shown. At the same time, the bunched ions may tend to defocus in the X-direction and Y-direction. To counteract this tendency, the apparatus 100 is equipped with a RF quadrupole arrangement 112, which arrangement may also be referred to as a quadrupole triplet. The RF quadrupole arrangement 112 includes a plurality of RF quadrupoles that are formed integrally within the different drift tubes including first grounded drift tube 102, second grounded drift tube 108, first powered drift tube 104, and second powered drift tube 106. A given RF quadrupole of the quadrupole arrangement 112 is defined by a given drift tube or pair of drift tubes, and in particular is formed by shaping of the surfaces of the drift tubes that face a given acceleration gap, as shown in
In the embodiment of
In accordance with embodiments of the disclosure, the plurality of quadrupoles of apparatus 100 are each arranged to defocus the ion beam 130 at a given gap (G1A, G1B, G1C) of the plurality of acceleration gaps along a first direction (either X-direction or Y-direction), extending perpendicular to a beam propagation direction (Z-axis, in the direction of the arrow). In other words, when the ion beam 130 traverses the gap G1A, gap G1B, and gap G1C, the ion beam is defocused at each of these gaps along the same direction (meaning parallel to the same axis). For example, the ion beam 130 may be defocused along the Y-direction at each of the gaps G1A, gap G1B, and gap G1C. Likewise, the plurality of quadrupoles of apparatus 100 are each arranged to focus the ion beam 130 at a given gap (G1A, G1B, G1C) of the plurality of acceleration gaps along a second direction, extending perpendicular to the beam propagation direction and to the first direction. In other words, following the above example where the ion beam is defocused along the Y-direction at each gap, the ion beam 130 may be focused along the X-direction at each of the gaps G1A, gap G1B, and gap G1C.
For purposes of concision, the arrangement of the apparatus 100 may be referred to hereinafter as a local “DODODO” (defocus-defocus-defocus) configuration, indicating for a given direction, such as the Y-direction, a defocusing (DO) of the ion beam takes place at three consecutive acceleration gaps. As a corollary, for the given local DODODO configuration with respect to the Y-direction, the apparatus 100 likewise provides a local FOFOFO (focus-focus-focus) configuration with respect to the X-direction, meaning that a focusing (FO) of the ion beam takes place at three consecutive acceleration gaps. As detailed further below, this novel configuration of a drift tube assembly provided by apparatus 100 may be combined with similar structures to assemble a linear accelerator whose beam focusing capability may be tuned according to given applications.
Turning now to
Note that the apparatus 150 may also be arranged to accept an ion beam (not shown) as a bunched ion beam, where upstream to the apparatus 100 the ion beam may be a continuous ion beam, and may be bunched by a buncher (not shown), arranged according to known LINACs. As such, by properly arranging the timing of the arrival of a bunch of ions of the ion beam at the gap G2A, gap G2B, the ion beam be accelerated by electric fields that are created when the generated RF voltage on the powered drift tube 154 reaches a maximum value and has the right polarity. In this manner, a given bunch may be accelerated generally along the Z-axis of the Cartesian coordinate system shown. To counteract the tendency of beam defocus, the apparatus 150 is equipped with a RF quadrupole arrangement 162 (a quadrupole doublet), connected to the drift tube assembly, and arranged circumferentially around the beam path, where the beam path is contained within the hollow cylinders that form the drift tube assembly of
A given RF quadrupole of the quadrupole that is defined by a given drift tube or pair of drift tubes is formed by shaping of the surfaces of the drift tubes that face a given acceleration gap, as shown in
In accordance with embodiments of the disclosure, the plurality of quadrupoles of apparatus 150 are each arranged to defocus an ion beam at a given gap (G2A, G2B) of the plurality of acceleration gaps along a first direction (either X-direction or Y-direction), extending perpendicular to a beam propagation direction (Z-axis). For example, the given ion beam may be defocused along the Y-direction at each of the gaps G2A, gap G2B. Likewise, the plurality of quadrupoles of apparatus 150 are each arranged to focus the ion beam at a given gap (G2A, G2B) of the plurality of acceleration gaps along a second direction, extending perpendicular to the beam propagation direction and to the first direction. In other words, following the above example where the ion beam is defocused along the Y-direction at each gap, the ion beam may be focused along the X-direction at each of the gaps G2A, gap G2B.
Following the convention of
In additional embodiments, the “DODO” or “DODODO” configurations may be extended to drift tube assemblies that have more than three gaps within a given acceleration stage. In other words, such drift tube assemblies will also exert a same quadrupole configuration for each acceleration gap of a drift tube assembly formed with four or more gaps.
The apparatus 170 is formed of a plurality of drift tubes, including a first grounded drift tube 172, a second grounded drift tube 180, a first powered drift tube 174, a second powered drift tube 176, and a third powered drift tube 178, disposed downstream of the second powered drift tube 176. It may be understood that the drift tube assembly formed by the apparatus 170 is coupled receive RF voltage signals at the three powered drift tubes (which drift tubes may be termed RF drift tubes), in a manner to generate time varying electric fields across the acceleration gap G3A, acceleration gap G3B, acceleration gap G3C, and acceleration gap G3D, in a manner designed to accelerate a passing bunched ion beam at each of these acceleration gaps.
At the same time, the bunched ions may tend to defocus in the X-direction and Y-direction. To counteract this tendency, the apparatus 170 is equipped with a RF quadrupole arrangement 182, which arrangement may also be referred to as a quadrupole quartet. The RF quadrupole arrangement 182 includes a plurality of RF quadrupoles that are formed integrally within the different drift tubes including first grounded drift tube 172, second grounded drift tube 180, first powered drift tube 174, and second powered drift tube 176, and third powered drift tube 178. A given RF quadrupole of the RF quadrupole arrangement 182 is defined by a given drift tube or pair of drift tubes as discussed previously. Thus, the RF quadrupole arrangement 182 for the given drift tubes of apparatus 170 is formed integrally as part of the apparatus 170. Similarly, to the previous embodiments, the quadrupole quartet of RF quadrupole arrangement 182 will exert a quadrupole effect that defocuses an ion beam along a given direction, such as the Y-direction, and focuses the ion beam along a direction orthogonal to the given direction, such as along the Y-direction, for each of the acceleration gap G3A, acceleration gap G3B, acceleration gap G3C, and acceleration gap G3D.
For purposes of concision, the arrangement of the apparatus 170 may be referred to hereinafter as a local “DODODODO” configuration, indicating for a given direction, such as the Y-direction, a defocusing (DO) of the ion beam takes place at four consecutive acceleration gaps. As a corollary, for the given local DODODODO configuration with respect to the Y-direction, the apparatus 170 likewise provides a local FOFOFOFO configuration with respect to the X-direction, meaning that a focusing (FO) of the ion beam takes place at four consecutive acceleration gaps.
A hallmark of the drift tube architecture 200 is that the orientation of the drift tube assembly 100A differs from the orientation of the drift tube assembly 100B. The drift tube assembly 100A may be seen to be rotated 90 degrees about the Y axis within the X-Y plane, with respect to the drift tube assembly 100B. As a consequence, the quadruple triplet formed in drift tube assembly 100A exerts a defocusing of an ion beam along a Y-direction at each of three acceleration gaps, while the quadrupole triplet formed in the drift tube assembly 100B exerts a defocusing of the ion beam along the X-direction, and a focusing effect along the Y-direction. Thus, with respect to the Y-direction, the drift tube assembly 100A exerts just a defocusing effect across all acceleration gaps, while the drift tube assembly 100B exerts just a focusing effect across all acceleration gaps. In this manner, the drift tube architecture 200 may be deemed to provide a global DOFO or FODO effect, where for a given direction, just defocusing takes place in the acceleration gaps of the drift tube assembly 100A and just focusing takes place in the acceleration gaps of the drift tube assembly 100B. Said differently, the drift tube architecture 200 combines a local DODODO structure (equivalent to a local FOFOFO structure) for each of two drift tube assemblies (corresponding to two acceleration stages) in order to generate a global FODO effect across the two acceleration stages.
By forming a local DODODO structure within a drift tube assembly of an acceleration stage, various embodiments facilitate more flexible control of beam shape and size. To emphasize this point,
As a consequence of this structure of
In accordance with embodiments of the disclosure, the overall focusing strength of a linear accelerator arranged with a local DODODO quadrupole structure may be tuned by varying certain parameters applied to the linear accelerator.
In
The variation of beam focusing as suggested in
In additional embodiments, phase control of signals applied to a drift tube assembly may be employed to control focusing strength.
As shown, the focusing strength of the DODODO arrangement of
The ion implanter 300 may include an analyzer 310, functioning to analyze the ion beam 306 as in known apparatus, by changing the trajectory of the ion beam 306, as shown. The ion implanter 300 may also include a buncher 312, and a linear accelerator 314 (shown in the dashed line), disposed downstream of the buncher 312, where the linear accelerator 314 is arranged to accelerate the ion beam 306 to form a high energy ion beam 315, having an energy greater than the ion energy of the ion beam 306, before entering the linear accelerator 314. The buncher 312 may receive the ion beam 306 as a continuous ion beam and output the ion beam 306 as a bunched ion beam to the linear accelerator 314. The linear accelerator 314 may include a plurality of acceleration stages (314-A, 314-B, . . . to 314-Z (not shown)), arranged in series, as shown. In various embodiments, the ion energy of the high energy ion beam 315 may represent the final ion energy for the ion beam 306, or approximately the final ion energy. In various embodiments, the ion implanter 300 may include additional components, such as filter magnet 316, a scanner 318, collimator 320, where the general functions of the scanner 318 and collimator 320 are well known and will not be described herein in further detail. As such, a high energy ion beam, represented by the high energy ion beam 315, may be delivered to an end station 322 for processing a substrate 324. Non-limiting energy ranges for the high energy ion beam 315 include 500 keV-10 MeV, where the ion energy of the ion beam 306 is increased in steps through the various acceleration stages of the linear accelerator 314. In accordance with various embodiments of the disclosure, one or more of the acceleration stages of the linear accelerator 314 may include a drift tube assembly, with integrated quadrupole arrangement, as detailed with respect to the embodiments of
While the aforementioned embodiments of linear accelerators focus on architecture where the orientation of drift tubes may vary from successive acceleration stages to generate an alternating sequence of local DODODO and local FOFOFO (see
In
Other quadrupole configurations are possible according to further embodiments, where the local structure within a single acceleration stage is varied, such as DODOFO, or DOFOFO, where the “global” quadrupole structure is varied, such as DDDFFF, DFODFO etc.
Moreover, in additional embodiments of the disclosure that encompass double gap acceleration stages (see, e.g.,
In view of the above, a first advantage afforded by the present embodiments is the avoidance of extra cost, greater beamline length, and greater complexity associated with known linear accelerators for ion implanters that employ a quadrupole apparatus for beam focusing that is separate from a drift tube assembly. Another advantage of the present embodiments is the ability to readily adjust focusing strength of the quadrupole arrangement by merely adjusting the RF phase of the ion beam or adjusting the RF voltage applied to an RF drift tube.
While certain embodiments of the disclosure have been described herein, the disclosure is not limited thereto, as the disclosure is as broad in scope as the art will allow and the specification may be read likewise. Therefore, the above description are not to be construed as limiting. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.
